The usual GPDs, \(K_i\) , parameterize the soft proton-proton matrix elements. However, for electroproduction
of charged pions proton-neutron transition matrix elements appear. With the help of SU(3) flavor symmetry
these transition GPDs and, hence, the corresponding form factors, can be related to the diagonal proton-proton
ones [1]}:
\(\gamma ^*p\rightarrow \pi ^+n:&& F_i^{\pi ^+}(t)\,=\,F_{i p\rightarrow n}(t)\,=\,F_i^u(t)-F_i^d(t)\,, \nonumber \\\gamma ^*n\rightarrow \pi ^-p:&& F_i^{\pi ^-}(t)\,=\,F_{i n\rightarrow p}(t)\,=\,F_i^u(t)-F_i^d(t)\,.\) 
